Prediction of in-situ fluid pH in high-acidity environments

¹ Research Institute of Natural Gas Technology, PetroChina Southwest Oil & Gasfield Company, Chengdu 610213, China
² National Energy R&D Center of High Sulfur Gas Exploitation, Chengdu 610000, China
³ High Sulfur Gas Exploitation Pilot Test Center, CNPC, Chengdu 610000, China
⁴ Southern Sichuan Gas District, PetroChina Southwest Oil & Gasfield Company, Luzhou 646000, China
⁵ Central Sichuan Oil and Gas District, PetroChina Southwest Oil & Gasfield Company, Suining 629000, China

^* Corresponding author’s e-mail: shencong202210@petrochina.com.cn

Abstract

In response to the difficulty of measuring fluid pH values in high-acidity, high-pressure, hightemperature, and complex ion environments, this paper proposes a predictive model for in-situ pH values in high-acidity environments. The model considers the influences of eleven factors, including ORP potential, temperature, and pressure, and is capable of calculating the pH value of fluids incorporating the following factors: pressure, temperature, Na⁺ ion concentration, K⁺ ion concentration, Ca²⁺ ion concentration, Mg²⁺ ion concentration, Cl^- ion concentration, HCO₃^- ion concentration, H₂S concentration, CO₂ concentration, and ORP potential. Furthermore, the model is optimized to possess variable adaptability, allowing compatibility with cases involving fewer than eleven influencing factors. Test results demonstrate that the predictive model for in-situ pH values in high-acidity environments exhibits high precision, with a maximum prediction error of 6.32%, a minimum of 1.19%, and an average prediction error of 4%. Compared to other existing models, it considers a more comprehensive set of factors, providing a mathematical approach to pH prediction that holds significance for corrosion control in oil and gas pipeline industries.